The Assignee of the present invention manufactures imprinters which are used for making imprints of a merchant's station plate and a credit card onto a formset for recording a credit transaction. Imprinters of this type have an extruded metal base which is made from aluminum and further a carriage which is a multiple piece element, including thermoplastically molded parts, to which are attached first and second rolling platens which respectively imprint the image of the station plate by moving the carriage in a first direction and the image of the credit card by moving the carriage in the opposite return direction. This type of imprinter is known as the double roller, double stroke imprinter in the industry.
U.S. Pat. Nos. 4,270,453 and 4,281,596 disclose a double rolling platen, double stroke imprinter having a carriage with first and second pairs of inclined slots mounted in downwardly extending sides which support the axles of a pair of rolling platens. For movement of the carriage in a direction in which one of the rolling platens is not imprinting, the slots function to guide the axle supporting the platen which is not imprinting upward so that the lifted rolling platen will roll over the station plate or credit card without imprinting character information onto the formset. However, for movement of the carriage in a direction in which one of the rolling platens is imprinting, the slots supporting the axle of the imprinting platen force the axle of the imprinting platen downward to exert imprinting pressure on the station plate or credit card to imprint characters onto the formset.
The carriage of the '453 and '596 patents transmits the force of imprinting transferred through the rolling platen axles to the top surface of the pair of slots contained within the side walls of the carriage to the bed of the imprinter and to the wheels riding on the base which support the carriage during the imprinting stroke. However, the carriage of the '453 and '596 patents is of a complex shape requiring precise dimensional tolerances to maintain proper spacing between the rolling platens and the flatbed. The clearance between the flatbed and the rolling platens is established by the axles of the rolling platens contacting the top surface of the aforementioned pairs of slots without any adjustment mechanism being provided for varying the height of the rolling platens. As a result, precise dimensional tolerance is required in the forming of the slots in the sides of the carriage to achieve an optical character readable (OCR) image. Manufacturing an imprinter with components having precise dimensional tolerances adds to its expense.
In order to obtain a high quality imprint which is OCR readable, it is necessary that a set range of clearance exist between the rolling platens and the base of the imprinter during imprinting. The wheels which support the carriage on the rails of the base must be adjusted to be spaced from each other within a set range so that unacceptable play orthogonal to the flatbed of the imprinter during imprinting, which would degrade the quality of the imprint, does not exist before the clearance between the rolling platens and flatbed can be set.
In the prior art imprinters with metallic carriages have been manufactured by various processes. Multiple stage piercing of flat plate has been used. Others, including the Assignee, have used steel strip, which is a. flat material, which does not permit internal features to be installed in the part without secondary addition of components requiring additional parts and labor. Such components include assembled roller brackets. More recently, carriages have been made by die casting which provides the ability to form internal features during the casting process which eliminates the requirement for additional parts. However, while die casting has the advantage of providing a complete assembly including internal parts with high dimensional tolerances, it has the disadvantage of being an expensive process.
The assignee's U.S. Pat. No. 5,385,094 discloses an improved imprinter and method of manufacturing and assembly thereof which achieves substantial cost savings of approximately 50% by utilizing an extrusion to form the carriage. This patent also discloses utilizing metal machining operations permitting cutout areas in the extrusion to be made prior to bending of the sides of the extrusion to form the opposed downwardly extending sides of the carriage which also contain a bendable rib to which the upper wheel of the carriage support is attached that is bent to set the spacing between the upper and lower wheels of the carriage. The patent also provides forming first and second pairs of openings which support axles of first and second rolling platens in the downwardly extending members of the extrusion in combination with first and second pairs of stops mounted in the carriage which are used for setting the spacing of the first and second rolling platens relative to the flatbed during movement of the carriage to imprint a station plate and credit card. The openings are formed with a length and a height which is greater than the diameter of the axles supporting the rolling platens so that contact of the outside periphery of the first and second rolling platens with a print bearing element, such as a station plate or credit card, forces the axles of the rolling platens orthogonally upward from the flatbed to engage the stops mounted in the carriage adjacent to first and second sides of the rolling platens to set the clearance required for the imprinting of a high quality OCR readable image and to provide clearance between the rolling platens and the credit card and station plate during movement in the nonimprinting direction permitting the rolling platens to be lifted from contact with the credit card or station plate without contacting the stops that prevents a double image from being imprinted. If substantial pressure is exerted between the rolling platen and the credit card and station plate during movement of the carriage in the nonimprinting direction, a double imprint can be produced which interferes with OCR reading. FIG. 15 of this patent shows an embodiment in which the openings have a first section which is parallel to the undersurface of the carriage and a second section which is inclined thereto.
However, it is still desired to provide an improved imprinter which can be manufactured with still further cost savings, and which has a simplified construction.